Added release notes for

• Return from ImagingFill early if image has a zero dimension #6842, largely copying https://pillow.readthedocs.io/en/stable/releasenotes/8.2.0.html#fix-memory-dos-in-imagefont, since the solution came from a new version of that problem
• Fixed null pointer dereference crash with malformed font #6846, which would have only been present since Pillow 8.0.0, when FT_Bitmap_Convert was added by Add support for CBDT and COLR fonts #4955.